1. Field of the Invention
The present invention relates to a nonlinear crystalline polyester which is used as a resin binder for a toner used for developing electrostatic latent images formed in electrophotography, electrostatic recording method, electrostatic printing, and the like, and a base material for mold materials used in core materials for automobile interior materials, silencers for air conditioners, fiber-reinforced plastics, soundproofing plates for construction materials, and the like.
2. Discussion of the Related Art
There have been known that a crystalline resin is suitably used as a resin binder for toner (Japanese Examined Patent Publication No. Sho 62-39428 and Japanese Patent Laid-Open Nos. Sho 62-276565 and Hei 9-329917). However, presently known crystalline resins are each found to be a linear polymer from its raw material monomers, so that there has not yet been reported a polyester which is nonlinear and crystalline.
An object of the present invention is to provide a nonlinear crystalline polyester having excellent fixing ability and appropriate strength when used as a resin binder for a toner for electrophotography, and a base material for mold materials.
The above object and other objects of the present invention will be apparent from the following description.
The present invention pertains to a nonlinear crystalline polyester obtained by polycondensing monomers containing trivalent or higher polyvalent monomers selected from the group consisting of trihydric or higher polyhydric alcohols and tricarboxylic or higher polycarboxylic acid compounds in an amount of from 0.1 to 20 mol % of all monomers used for polycondensation.
The nonlinear crystalline polyester of the present invention is prepared by using monomers containing an alcohol component comprising a dihydric alcohol and/or a trihydric or higher polyhydric alcohol, and a carboxylic acid component comprising a dicarboxylic acid compound and/or a tricarboxylic or higher polycarboxylic acid compound.
The dihydric alcohol components include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like, among which from the viewpoints of the softening point and the crystallinity of the resin, 1,4-butanediol, ethylene glycol, 1,2-propylene glycol, and 1,6-hexanediol are preferable, and 1,4-butanediol is more preferable. Especially, it is desirable that 1,4-butanediol constitutes preferably 80 mol % or more, more preferably from 90 to 100 mol %, of the alcohol component.
The trihydric or higher polyhydric alcohols include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene, and the like, among which glycerol is preferable from the viewpoints of the softening point and the crystallinity of the resin.
In addition, examples of the dicarboxylic acid compounds include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, and malonic acid; succinic acids substituted by an alkyl group having 1 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms, such as dodecenylsuccinic acid and octylsuccinic acid; acid anhydrides thereof, alkyl (1 to 3 carbon atoms) esters thereof, and the like, among which from the viewpoints of the softening point and the crystallinity of the resin, fumaric acid, succinic acid and adipic acid are preferable, and fumaric acid is more preferable. Especially, it is desirable that fumaric acid constitutes preferably 80 mol % or more, more preferably from 85 to 100 mol %, of the carboxylic acid component.
Examples of the tricarboxylic or higher polycarboxylic acid compound include 1,2,4-benzenetricarboxylic acid (trimellific acid), 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxy-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, Empol trimer acid, acid anhydrides thereof, alkyl (1 to 3 carbon atoms) esters thereof, and the like, among which from the viewpoints of the softening point and the crystallinity of the resin, trimellitic acid and derivatives thereof are preferable, and trimellitic acid anhydride is more preferable.
In the present invention, in order to form a nonlinear polyester, monomers contain trivalent or higher polyvalent monomers selected from the group consisting of trihydric or higher polyhydric alcohols and tricarboxylic or higher polycarboxylic acid compounds in an amount of from 0.1 to 20 mol %, preferably from 0.5 to 15 mol %, more preferably from 1 to 13 mol %, of all monomers used for polycondensation.
The polycondensation of the alcohol component with the carboxylic acid component can be carried out, for instance, by the reaction at a temperature of from 150xc2x0 to 250xc2x0 C. in an inert gas atmosphere, using an esterification catalyst and a polymerization inhibitor as occasion demands. Concretely, in order to enhance the strength of the resin, the entire monomers may be charged at once. Alternatively, in order to reduce the low-molecular weight components, divalent monomers are firstly reacted, and thereafter trivalent or higher polyvalent monomers are added and reacted.
One of the great features of the polyester obtainable by the polycondensation of the above monomers resides in that the polyester is nonlinear and crystalline. In other words, the polyester of the present invention is nonlinear, thereby exhibiting excellent strength, and is crystalline, thereby exhibiting excellent fixing ability when the polyester is used as a resin binder for toners or a base material for mold materials. Therefore, the polyester of the present invention can be suitably used for toners for electrophotography, molding materials, and the like.
In the present invention, the term xe2x80x9cnonlinearxe2x80x9d may take any non-linear structure, including branched structures and cross-linked structures. Also, the term xe2x80x9ccrystallinexe2x80x9d means that a Ta/Tb ratio, each as defined as follows, is from 0.9 to 1.1, preferably from 0.98 to 1.05. Here, in the present invention, Ta refers to a temperature corresponding to xc2xd of the height (h) of the S-shaped curve showing the relationship between the downward movement of a plunger (flow length) and temperature, namely, a temperature at which a half of the resin flows out, when measured by using a flow tester of the xe2x80x9ckokaxe2x80x9d type (xe2x80x9cCFT-500D,xe2x80x9d manufactured by Shimadzu Corporation) in which a 1 g sample is extruded through a nozzle having a dice pore size of 1 mm and a length of 1 mm, while heating the sample so as to raise the temperature at a rate of 6xc2x0 C./min and applying a load of 1.96 MPa thereto with the plunger, which is also called a softening point. Also, Tb refers to the temperature of an intersection of the extension of the baseline of not more than the maximum endothermic peak temperature and the tangential line showing the maximum inclination between the kickoff of the peak and the top of curves as determined with a sample using a differential scanning calorimeter (xe2x80x9cDSC Model 210,xe2x80x9d manufactured by Seiko Instruments, Inc.), when the sample is treated by raising its temperature to 200xc2x0 C., cooling the hot sample at a cooling rate of 10xc2x0 C./min. to 0xc2x0 C., and thereafter heating the sample so as to raise the temperature at a rate of 10xc2x0 C./min.
In consideration of its use as a resin binder for toners, and the like, the polyester of the present invention has Ta, namely the softening point, of preferably from 85xc2x0 to 140xc2x0 C., more preferably from 100xc2x0 to 140xc2x0 C., and Tb of preferably from 77xc2x0 to 150xc2x0 C., more preferably from 90xc2x0 to 140xc2x0 C.
In consideration of its use as a resin binder for toners, and the like, the nonlinear crystalline polyester has a number-average molecular weight of tetrahydrofuran-soluble component of preferably from 500 to 3000.